poj 2253Frogger

Description

Freddy Frog is sitting on a stone in the middle of a lake. Suddenly he notices Fiona Frog who is sitting on another stone. He plans to visit her, but since the water is dirty and full of tourists' sunscreen, he wants to avoid swimming and instead reach her by jumping. 
Unfortunately Fiona's stone is out of his jump range. Therefore Freddy considers to use other stones as intermediate stops and reach her by a sequence of several small jumps. 
To execute a given sequence of jumps, a frog's jump range obviously must be at least as long as the longest jump occuring in the sequence. 
The frog distance (humans also call it minimax distance) between two stones therefore is defined as the minimum necessary jump range over all possible paths between the two stones. 

You are given the coordinates of Freddy's stone, Fiona's stone and all other stones in the lake. Your job is to compute the frog distance between Freddy's and Fiona's stone. 

Input

The input will contain one or more test cases. The first line of each test case will contain the number of stones n (2<=n<=200). The next n lines each contain two integers xi,yi (0 <= xi,yi <= 1000) representing the coordinates of stone #i. Stone #1 is Freddy's stone, stone #2 is Fiona's stone, the other n-2 stones are unoccupied. There's a blank line following each test case. Input is terminated by a value of zero (0) for n.

Output

For each test case, print a line saying "Scenario #x" and a line saying "Frog Distance = y" where x is replaced by the test case number (they are numbered from 1) and y is replaced by the appropriate real number, printed to three decimals. Put a blank line after each test case, even after the last one.

Sample Input

2
0 0
3 4

3
17 4
19 4
18 5

0

Sample Output

Scenario #1
Frog Distance = 5.000

Scenario #2
Frog Distance = 1.414

给出两只青蛙的坐标A、B，和其他的n-2个坐标，任一两个坐标点间都是双向连通的。显然从A到B存在至少一条的通路，每一条通路的元素都是这条通路中前后两个点的距离，这些距离中又有一个最大距离。现在要求求出所有通路的最大距离，并把这些最大距离作比较，把最小的一个最大距离作为青蛙的最小跳远距离。
用dijkstra变形即可；
核心：

 dis[j]=min((max(dis[now],map[now][j])),dis[j]);

#include <stdio.h>
#include <string.h>
#include <math.h>
#define INF 0x7f7f7f7
double map[210][210];
double dis[210];
int vis[210],n;
double min(double a,double b)
{
    return a<b?a:b;
}
double max(double a,double b)
{
    return a>b?a:b;
}
void dijkstra()
{
    int i,now,j,minn;
    vis[0]=1;
    for(i=0;i<n;i++)
        dis[i]=map[0][i];
    for(i=1;i<n;i++)
    {
        minn=INF;
        for(j=0;j<n;j++)
        {
            if(!vis[j]&&dis[j]<minn)
            {
                minn=dis[j];
                now=j;
            }
        }
        vis[now]=1;
        for(j=0;j<n;j++)
            if(!vis[j])
                dis[j]=min((max(dis[now],map[now][j])),dis[j]);
    }
    printf("%.3lf\n",sqrt(dis[1]));
    printf("\n");
}
int main()
{
    int i,j,cas=1;
    double a[210],b[210];
    while(scanf("%d",&n)&&n)
    {
        for(i=0;i<n;i++)
            scanf("%lf%lf",&a[i],&b[i]);
        for(i=0;i<n;i++)
            for(j=i+1;j<n;j++)
               map[j][i]=map[i][j]=(a[i]-a[j])*(a[i]-a[j])+
                            (b[i]-b[j])*(b[i]-b[j]);
        memset(vis,0,sizeof(vis));
        printf("Scenario #%d\n",cas++);
        printf("Frog Distance = ");
        dijkstra();
    }
    return 0;
}